Generating methanol using ultrapure, high pressure hydrogen

ABSTRACT

In various implementations, methanol is produced using a (CO+H 2 ) containing synthesis gas produced from a combined PDX plus EHTR or a combined ATR plus EHTR at a pressure of 70 bar to 100 bar at the correct stoichiometric composition for methanol synthesis so that no feed gas compressor is required for the feed to the methanol synthesis reactor loop.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application No. 61/348,027, filed May 25, 2010, the entiredisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to producing methanol and, moreparticularly, to producing methanol using a carbon monoxide plushydrogen (CO+H₂) synthesis gas mixture produced at a pressure above thepressure required in the methanol synthesis reactor without anysubsequent compression.

BACKGROUND

Methanol, also known as methyl alcohol, wood alcohol, wood naphtha orwood spirits, is a simple alcohol, with the formula CH₃OH, that is alight volatile flammable poisonous liquid alcohol. Methanol hasextensive uses in the production of a range of chemicals includingethylene glycol, acetic acid, vinyl acetate. Methanol may also be usedfor producing biodiesel via trans-esterification reaction. Methanol isproduced naturally in the anaerobic metabolism of many varieties ofbacteria and is ubiquitous in the environment. Methanol is producedcommercially by combining CO and CO₂ with hydrogen in a catalyticreactor operating at pressures typically in the range 70 to 100 bar andtemperatures in the range 250° C. to 300° C. Commonly used methods ofproducing the CO+H₂ synthesis gas from natural gas includesteam/hydrocarbon catalytic reforming (SMR), catalytic auto-thermalreforming (ATR), partial oxidation (POX), and combinations of theforgoing. A combination of the ATR and a convectively heated SMR is thebasis of the well known Leading Concept Ammonia Process. The synthesisgas generation system is described in a paper “A Methanol Technology forthe 20^(th) Century” by R Kirkpatrick and T Fitzpatrick presented at theWorld Methanol Conference San Diego November 1999. In each case exceptPOX, the synthesis gas from the optimum generation pressure iscompressed to the higher pressure required by the methanol reactorsystem. POX can produce syngas at pressures in the range 70 to 100 barbut it is not an economic method in isolation since it producessynthesis gas at a very high temperature of 1300° C. to 1400° C. andthere is a large specific oxygen requirement.

SUMMARY

In various implementations, methanol is produced using CO+H₂+CO₂synthesis gas produced using the basic combination of POX+EHTR (EnhancedHeat Transfer Reformer) which can produce methanol according to thefollowing reactions:CO+2H₂═CH₃OHCO2+3H₂═CH₃OH+H₂OSynthesis gas can be produced at a pressure in the range 70 bar to 100bar with a methane content which does not exceed 2% molar (dry basis).The combination of a POX+EHTR using a gas turbine may provide the powerfor the oxygen plant air compressors as described in U.S. Pat. Nos.6,534,551 and 6,669,744. Providing the power the gas turbine may resultin a combination of heat recovery in the synthesis gas generation systemand in the circulating methanol synthesis reactor loop, which may resultin optimum or otherwise increased heat recovery and may providesubstantially all of the shaft power and process heat for synthesis gasgeneration, methanol synthesis, and methanol purification systems. Thecombustible effluents discharged from the methanol purification systemmay be incinerated at near atmospheric pressure in the gas turbineexhaust fired heater, which may produce heating for the steam andnatural gas feeds to the POX+EHTR synthesis gas generation system. Thishighly efficient use for these combustible effluents may replace naturalgas feed on an equivalent heat release basis. The combustible effluentsmay include at least one of a fusel oil, purge gas from the loop, orvent gas from distillation and pressure let down vessel.

In some implementations, the methanol-producing system can include a POXplus EHTR with very high steam to active carbon ratio in the EHTRreformer feed, which may produce a synthesis gas mixture leaving thewaste heat boiler at temperatures from 300° C. to 400° C. and a pressurefrom 70 bar to 100 bar. The steam to active carbon ratio in the EHTRfeed stream can typically be in the range of about 5 to 8 such as therange of about 5.5 to 6.5. To achieve a methane content in the drysyngas of less than 2% molar, the EHTR may operate at a high steam toactive carbon ratio. In order to operate the EHTR in combination with aPOX reactor to maximize or otherwise increase syngas output from a giventotal natural gas feed, the POX may be operated with a much higher thannormal ratio of oxygen to natural gas. Normal operation of a POX systemwith oxygen gives good performance with methane content in the exit gason a dry basis in the range 0.25% to 0.5% molar when the POX dischargetemperature is in the range of 1300 to 1350° C. The POX reactor mayresult in an outlet temperature of between 1400° C. and 1500° C. withnatural gas feed. An example uses a steam to active carbon ratio of 6.03in the EHTR, which may have an outlet shell side temperature of about600° C., a tube side exit temperature of about 900° C., a POX outlettemperature of about 1446° C. and a mixed shell side inlet temperatureon the EHTR shell side of about 1131° C. The waste heat boiler outletsyngas temperature may be about 320° C. and the syngas pressure may beabout 77 bar. The syngas may contain approximately the followingcomponents: (1) CO lb mols 1806.31; and (2) CO₂ lb mols 351.18. Forstoichiometry in the production of methanol, these components mayinclude about 3×351.18+2×1806.31=4666.16 lb mols H₂. The actual contentmay be about 4559.56 lb mols, which may allow for the small excess ofCO+CO₂.

The syngas leaving the waste heat boiler may be cooled in a first heatexchanger against condensate and then against deoxygenated boilerfeed-water. The cooled syngas may then be cooled against an ambientcooling system such as cooling water to a temperature at which the watercontent is largely in the liquid phase. The water may be separated as itadversely effects the equilibrium composition and conversion of syngasto methanol per pass of the syngas through the methanol reactor. Thepressure of the steam generated in the waste heat boiler may beconsiderably higher than the steam pressure used for the feed to theEHTR. The saturated steam produced in the waste heat boiler may besuperheated in the gas turbine exhaust fired heater and may be reducedin pressure for the EHTR to produce excess power in a pass-out steamturbine. The pass-out steam may be further superheated in the heater toa temperature in the range 450° C. to 550° C. before or after mixingwith the feed to the methanol synthesis gas loop at a pressuresubstantially equal to a pressure for the direct feed to the methanolloop with substantially no additional gas compression. In addition, thewater content can typically be in the range of about 0.1 to 0.15% molar,and the methane content may be below 2%. This combination of propertiesmay result in an ideal syngas feed to the methanol loop. All flammableeffluents from the methanol loop may be combusted efficiently in the gasturbine fired heater. Using a gas turbine drive for the oxygen plant aircompressor drive system may result in the methanol plant not usingstand-by steam boilers to generate the steam for the compressor drivesystems, which are generally steam turbine driven in existing methanolplants. The proposed POX-EHTR combination with the features shown is anefficient method at present developed for the production of syngas formethanol synthesis.

Operation of the methanol loop may be entirely from this point onwards.The heat generated in the methanol synthesis reaction may beconventionally recovered and partly or wholly used to provide the heatfor operation of the methanol purification distillation system. Excesssteam at medium to low pressure may be used to produce excess power in acondensing steam turbine, which may be added to the passout steamturbine. The details of one or more implementations are set forth in theaccompanying drawings and the description below.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example system for the production of synthesis gasfor a methanol plant.

FIG. 2 illustrates a detailed flow scheme for the production ofsynthesis gas for a methanol plant.

FIG. 3 illustrates stream compositions flows temperatures and pressuresfor an example of a feed stream being processed by the systemillustrated in FIG. 2.

FIG. 4 illustrates another example system for the production ofsynthesis gas for a methanol plant.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In various implementations, a feed stream can be processed to produce asynthesis gas for methanol production which may have one or more of thefollowing characteristics: a stoichiometric ratio of H₂ to (CO+CO₂) formethanol production; a production pressure in the range of about 70 barto 100 bar which may not include further compression to feed thesynthesis gas directly into the methanol reactor loop; a synthesis gaswith less than about 2% molar methane content; a synthesis gas with lessthan about 0.2% molar water content; combustible effluents from themethanol production and a purification system that returns to them tosynthesis gas production process for combustion; returning excess steamproduced by the methanol production and purification process to thesynthesis gas production process where it can be used to produce power;and/or others. The processed feed streams may include a variety of feedstreams that include methane, such as natural gas, hydrocarbon fuels,methane rich gases such as coal-bed methane or biogas (e.g., streamproduced from the anaerobic decay of matter). The feed streams mayinclude liquid hydrocarbon streams.

The following description provides examples of operating temperatures,pressures and concentrations in connection with describing the methanolsystems and operations. These values are for illustration purposes onlyand the invention may use some, all or none of these values withoutdeparting from the scope of this disclosure.

FIG. 1 is a flow chart illustrating an method 100 for generatingmethanol in accordance with some implementations of the presentdisclosure. Generally, the method 100 describes an example technique forusing purge gas from a methanol loop as a feed stream to a gas turbine.Method 100 contemplates using any appropriate combination andarrangement of logical elements implementing some or all of thedescribed functionality.

Method 100 begins at step 102 where oxygen is produced in an airseparation plant with air compressors driven by a gas turbine. At step104, exhaust from the gas turbine is used in a heat exchanger forheating steam, water, and methane preheat. Methane and oxygen arereacted in a POX at a temperature greater than about 1400° C. at step106. Next, at step 108, heat from the product streams of the POX andEHTR are used to heat the EHTR tubes. In connection with recycling theheat, steam and methane are reacted at ratio greater than about 5 to 1in a convectively heated catalytic tubular reformer (e.g., EHTR) at step110. Next, at step 112, steam is produced using heat recovered fromcooling syngas in a waste heat boiler. In addition, heat is recoveredfrom cooling syngas for condensate and boiler feed-water preheating atstep 114. At step 116, water is separated from the cooled syngas toproduce methanol plant feed at reaction loop pressure with less thanabout 2% CH₄ and less than about 0.2% H₂0, Next, at step 118, the streamis passed to the methanol plant and methanol purification. Methanolplant combustible effluent plus methane used as gas turbine exhaustheater fuel at step 120.

FIG. 2 is a detailed flow scheme showing the syngas, methanol, energysystem and water treatment system in accordance with someimplementations of the present disclosure. Pre-heated feed streams 5 and6 may be introduced into synthesis gas generation systems 4 and 53. Forexample, a feed stream, such as natural gas, may be introduced to aPOX/EHTR synthesis gas generation system, as illustrated, that includesa Partial Oxidation Reactor (POX) combined with a Gas Heated CatalyticReformer (EHTR), in which the combined POX product gas and the productgas from the EHTR are used to provide the total or at least asubstantial portion of the heat requirement of the convectively heatedEHTR. As illustrated, a compressed heated oxygen stream 2 may begenerated in a pumped liquid oxygen cryogenic Air Separation Unit (ASU)3. The oxygen stream 2 may be preheated (e.g., by heat from condensingsteam stream 14. and provided to a POX with a natural gas feed stream 5.A gas turbine 15 may drive an air compressor 18, which may provide thefeed air stream 16 at about 5.8 bar to the ASU 3. A portion of the feedair stream 16 is further compressed to, for example, about 70 bar in abooster compressor 19. The booster compressor 19 may be driven by anelectric motor which derives its electric power from a generator coupledto the gas turbine 15. A portion of the feed stream (e.g., natural gas)46 may be provided to the gas turbine 15 as fuel. Stream 46 may comprisenatural gas mixed with methanol loop purge gas stream 23 derived fromthe methanol plant and suitably reduced in pressure. It is preheated toa temperature of, for example, about 250° C. The gas turbine exhaust 20may be at, for example, approximately 537° C. The gas turbine exhaust20, which may include oxygen, may be provided as the combustion airstream for the fired heater burner 21 which uses a combination of 2 fuelstreams. Firstly the low pressure gaseous combustible effluent from themethanol plant and secondly a combustible liquid fuel stream 22 from themethanol plant. The combustion product 29 from the burner 21 enters theconvection section of the fired heater 28. The cooled exhaust gas 30 isdischarged from the heater to the atmosphere at a temperature of, forexample, about 137° C.

The natural gas feed stream 54 at 40 bar is compressed to 82 bar incompressor 55 and enters the heater as stream 25 at 80° C. This streamis heated to 500° C. and divided into stream 5, the POX feed and stream26 which may be mixed with the superheated steam stream 47 at about 500°C. The combined stream 6 is the feed to the catalyst filled tubes of theEHTR. A sidestream of natural gas preheated to 320° C. is taken off toform part of the gas turbine fuel stream 46.

In the POX 4, the natural gas stream 5 may be partially oxidized withoxygen stream 2 to produce synthesis gas stream 27 (e.g., a stream thatincludes hydrogen and carbon monoxide). The synthesis gas stream 27 mayinclude unreacted feed from the natural gas stream 5 and/or byproductssuch as carbon dioxide, methane, nitrogen, argon, oxygen, and watervapor. The synthesis gas stream 27 is at a temperature of 1446° C. andenters the shell side of the EHTR reactor 53. This temperature may bemuch higher than the normal exit temperature of a natural gas fed POXreactor which would be about 1345° C. The excess heat present in the POXexit gas due to the higher temperature may allow the EHTR to be operatedat a pressure of 80 bar with a steam to active carbon ratio of 6.03 sothat the total outlet flow from the POX plus the EHTR stream 7 may havea methane concentration of 1.8% molar (dry basis).

In some implementations, a stream 6 including a mixture of natural gasand/or steam (e.g., at approximately 500° C.) may also be fed into theEHTR. The mixture of natural gas and steam may flow downwards throughthe catalyst in the EHTR (e.g., catalyst filled vertical open endedtubes) and may exit the EHTR tubes as a mixture of hydrogen and carbonmonoxide plus some carbon dioxide, methane, nitrogen, argon and watervapor. This gas may exit at approximately 900° C. This gas stream mayalso mix with the product gas stream 27 from the POX. The combinedstream (e.g., gas exiting the catalyst tubes mixed with the productstream from the POX) may flow upwards through the shell side of the EHTRand/or may provide the heat required for the steam/hydrocarbon reformingreactions. The product gas stream 7 may exit the EHTR at approximately600° C. The product gas stream 7 may include synthesis gas and may becooled to produce a cooled stream 8. The product gas stream 7 may becooled in a waste heat boiler from 600° C. to 340° C. producing steamstream 41 from a preheated boiler feedwater stream 56. The steam stream41 at 330° C. and 125 bar exiting the waste heat boiler 30 issuperheated to 500° C. as it passes though the fired heater 28 exitingas stream 42. This stream enters a pass-out turbine 44 where itspressure is reduced to 80.5 bar at a temperature of 432° C. The exitstream divides. Stream 14 is condensed in the oxygen heater 48, whilethe remainder, stream 45, enters the fired heater 28 and is heated to,for example, 500° C. Stream 47 then mixes with the preheated natural gasstream 26, becoming the EHTR tube side feed stream 6. The syngas stream8 is cooled in heat exchanger 31 to 201° C. while heating the boilerfeed water stream 51 to 310° C. There may be a large quantity ofuncondensed steam present in stream 9. The syngas is cooled to, forexample, 164° C. in heat exchanger 57 which may be used to preheat andevaporate a boiler feed water stream 35 at, for example, 6.9 bar whichleaves as stream 36 to enter the fired heater 28 where its temperatureis raised to, for example, 330° C. Stream 52 produces power in thecondensing steam turbine 50. The condensed water stream 58 together withall, substantially all or other water streams enter the waterpurification and treatment system 37. A treated water stream 48 may bedischarged from the system. The syngas stream 24 is then cooled to 40°C. against heating cooling water streams 11 to 12 in heat exchanger 59.Condensed water is separated in 33 and the syngas stream 13 enters themethanol synthesis loop and purification system 38. Substantially puremethanol may be produced at a rate of, for example, about 730 metrictons/day as stream 39. The syngas stream 13 may be reheated in 59 to150° C. before entering the methanol loop to increase the excess steamproduction from the methanol synthesis and purification system.

In general, the feed stream 5 may undergo partial oxidation (eqn 1) in aPOX reactor, for example. In addition, some total oxidation (eqn 2) mayoccur, and there may be a shift reaction (eqn 4). The reactions mayinclude:CH₄+½O₂→CO+2H₂—  (1)CH₄+2O₂→CO₂+2H₂O—  (2)The product synthesis gas from the POX reactions produces a very hightemperature gas mixture that may be used to provide part of theendothermic heat of reaction for steam/hydrocarbon reforming in asecondary downstream convectively heated catalytic reformer (EHTR). Theremaining part of the heat requirement is provided by mixing the productgas from the EHTR tubes at 900° C. with the product gas from the POX at1446° C. prior to the total gas stream being used to heat the GHR. Thesteam reforming reactions may include:CH₄+H₂O→CO+3H₂—  (3)CO+H₂O→CO₂+H₂—  (4)The synthesis gas stream 7 may include hydrogen and carbon monoxide. Thesynthesis gas stream 7 may also include methane, water vapour, carbondioxide, argon, and/or nitrogen. The relative concentrations of carbonmonoxide and hydrogen may depend, for example, on the hydrocarbon feedcomposition (e.g., methane is only used in these equations forsimplicity, but other components may be present in the feed and beoxidized and/or reformed), pressure, POX outlet temperature. EHTRcatalyst tube outlet temperature, the feed temperature of oxygen,natural gas and steam to POX and EHTR, the steam to active carbon ratioin the feed to the EHTR and the shell side outlet temperature from theEHTR. The oxygen purity can be in the range 90 to near 100% by volume O₂and, more particularly, can be in the range 95% to 99.5% O₂ by volume.The ideal oxygen purity is in the range 99% to 99.9% molar to minimizemethanol loop purge gas loss.

In some implementations, methanol is produced directly from thesynthesis gas generation system at high purity (e.g., 95% or greater).Operation of the proposed syngas generation system may be carried out atpressures in the range 70 bar to 100 bar which may allow the producedsynthesis gas to enter the circulating methanol synthesis reactor loopindependent or without using a feed gas compressor. Reactions 1 to 3 areadversely affected by higher pressures, while reaction 4 is independentof pressure. Reactions 1 and 2 may compensate for higher pressure by theincrease in reaction temperature, which may be achieved through a slightincrease in the oxygen to hydrocarbon ratio in the POX feed. Theincrease in the oxygen to hydrocarbon ratio and the increase intemperature will not cause significant problems in the design of theequipment.

In order for the EHTR system to operate as a steam/hydrocarbon reformingreactor at high pressures above 70 bar, the system 100 may use a veryhigh steam to active carbon ratio in the feed to the GHR in order tocontrol the methane concentration in the synthesis gas product 7. Thismay be in the range 5 to 8 and such as the range 5.5 to 6.5. The actualsteam to active carbon ratio in the feed to the GHR depends on thepressure and the GHR catalyst tube outlet temperature. The ratio may bechosen to limit the ratio of CH₄ to (H₂+CO) in the synthesis gas productleaving the GHR tubes to at least about 5% such as in the range 5% to10% (molar). This may result in a methane concentration in the syngasproduct stream 7 below 2% molar (dry basis). In order to compensate forthe extra heat load on the EHTR, the POX outlet temperature may behigher than a normal figure of about 1340° C. The POX outlet temperaturemay be raised by increasing the oxygen to hydrocarbon ratio in the POXfeed so that the POX outlet temperature is above, for example, 1400° C.such as in the range 1425° C. to 1500° C. When using an ATR, the outlettemperature may be in general below 1050° C. and in this case the ratioof synthesis gas from the ATR to that from the EHTR may be increased.

In order for the EHTR system to operate as a steam/hydrocarbon reformingreactor at high pressures (e.g., above 70 bar), a very high steam toactive carbon ratio in the feed may be used. Thus, for the production ofsynthesis gas, a higher methane content in the outlet gas from the EHTRmay be produced. However, the outlet gas stream from the POX may nothave a higher methane content because it is operating at a higherdischarge temperature. Since about 70% of the syngas is produced fromthe POX reactor and only about 30% from the EHTR, it is possible totolerate a much larger CH₄ content in the GHR outlet gas than from, forexample, a stand-alone steam/natural gas reformer. Although it is notpossible to increase the outlet temperature from the ATR, the outlettemperature of greater than 1000° C. means that the CH₄ content may beless than 1% in the pressure range 70 bar to 100 bar, so an increasecaused by the desire to increase the reaction pressure may not have asignificant effect. It is however preferably to use the POX/EHTRcombination as this gives lower methane concentration in the syngas feedto the methanol loop and thus minimizes or otherwise reduce loop purgegas loss. A further characteristic of the EHTR design used in thisprocess is the fact that the EHTR catalyst filled tubes are mounted in avertical bundle with an inlet tube sheet at the top colder end, and withthe bottom hot outlet ends open, so that the tubes are free to expanddownwards when heated to operating outlet temperatures, which may be inthe range 800° C. to 900° C. This means that the pressure differencebetween the inside and outside of the GHR tubes, when operating atdesign conditions, may be small. The sum of the pressure drop in thecatalyst filled tube plus the shell side pressure drop may have amaximum value at the cold upper end of the GHR tubes and approximatelyzero at the bottom hot end of the tubes. The GHR may operate at anypressure up to an economic limitation caused by the pressure vesseldesign and any pressure constraint in the gas purification system chosencaused by the progressively higher gas pressure. In someimplementations, this operation can be different from a steam/naturalgas reformer, where the furnace operates at near atmospheric pressure,and the strength of the tubes imposes a pressure limitation on thesynthesis gas pressure which is generally below 35 to 40 atm. Thesefeatures may produce the CO+CO₂+H₂ feed gas for a low pressure methanolsynthesis system operating at a loop pressure in the range 70 to 100bar.

The benefits of this disclosure are that the overall efficiency of themethanol plant may be increased and cost may be reduced by operating thesynthesis gas system at high pressure, which may reduce equipment sizeand cost. In addition, the methanol system substantially eliminate theconventional synthesis gas compression system and introduces hot feedgas into the loop and may allow extra by-product power production.

FIG. 3 illustrates a chart 300 including operating conditions for themethanol system of FIG. 1. Based on the conditions defined in chart 300and the flow-sheet in FIG. 2, the system may include one or more of thefollowing performance characteristics: methanol production at about 730metric ton/day; total natural gas feed at about 828.26 million BTU/day(LHV basis); specific heat rate at about 26.43 million BTU (LHV basis)per metric ton methanol; oxygen flow at about 364 metric tons/day at99.5% molar purity 85 bar; and/or others. In some implementations, thechart 300 may be based on the use of a Siemens SGT-300 Gas Turbine.Having a notional efficiency of about 55% (LHV basis) for about 3.9 Mwexport power, the thermal efficiency of methanol production may be about71.5% (LHV basis).

FIG. 4 illustrates another example of a methanol system 400 thatintegrates the syngas system with the heat exchange. As previouslystated, a feed stream is, in various implementations, processed toproduce high pressure (e.g., greater than approximately 70 bars) syngasstreams comprising mixtures of CO+CO₂+H₂ suitable in composition for theproduction of methanol in, for example, an acatalytic process. Theprocessed feed streams may include a variety of feed streams thatinclude methane, such as natural gas, hydrocarbon fuels, methane richgases such as coalbed methane or biogas (e.g., stream produced from theanaerobic decay of matter). The feed streams may include liquidhydrocarbon streams. A pre-heated feed stream 405 may be introduced intosynthesis gas generation systems 404 and 407. For example, a feedstream, such as natural gas, may be introduced to a POX/EHTR synthesisgas generation system, as illustrated, that includes a Partial OxidationReactor (POX) combined with a Gas Heated Catalytic Reformer (EHTR), inwhich the combined POX product gas and the product gas from the EHTR areused to provide the total or at least a substantial portion of the heatrequirement of the EHTR. As another example, the feed stream may be fedinto an ATR/EHTR combined synthesis gas generation system that includesan Autothermal Reformer (ATR) combined with a EHTR, in which thecombined ATR product gas and gas from the EHTR are used to provide thetotal or at least a substantial portion of the heat requirement of theEHTR. As illustrated, a compressed oxygen stream 402 may be generated ina pumped liquid oxygen cryogenic Air Separation Unit (ASU). The oxygenstream 402 may be preheated (e.g., by heat from steam heated by fuel 438combusted in a fired heater burner), and provided to a POX with anatural gas feed stream 405. The natural gas feed stream 405 may bepreheated (e.g., by heat generated by a fuel 438 and/or natural gas 447,such as natural gas from the feed stream, combusted in a fired heaterburner).

In the POX, the natural gas stream 405 may be partially oxidized toproduce synthesis gas stream 404 (e.g., a stream that includes hydrogenand carbon monoxide). The synthesis gas stream 404 may include unreactedfeed from the natural gas stream 405 and/or byproducts such as carbondioxide, methane, nitrogen, oxygen, and water vapor. The synthesis gasstream 404 may enter the shell side of the EHTR 407.

In some implementations, a stream 406 including a mixture of natural gasand/or steam (e.g., at approximately 550° C.) may also be fed into theEHTR. The stream 406 may be preheated (e.g., by heat generated by fuel438 combusted in a fired heater burner). The mixture of natural gas andsteam may flow downwards through the catalyst in the EHTR (e.g.,catalyst filled vertical open ended tubes) and may exit the EHTR as amixture of hydrogen and carbon dioxide plus some carbon monoxide,nitrogen, argon and water vapor. This gas may exit at approximately 900°C. This gas stream may also mix with the product gas stream 404 from thePOX. The combined stream (e.g., gas exiting the catalyst tubes mixedwith the product stream from the POX) may flow upwards through the shellside of the EHTR and/or may provide the heat required for thesteam/hydrocarbon reforming reactions. The product gas stream 407 mayexit the GHR at approximately 600° C. The product gas stream 407 mayinclude synthesis gas and may be cooled to produce a cooled stream 408.The product gas stream 407 may be cooled in a waste heat boilerproducing steam stream 431 from a preheated boiler feedwater stream 429.The steam stream 431 exiting the waste heat boiler may include saturatedsteam and may be superheated as it passes though the fired heater.

In general, the feed stream 405 may undergo partial oxidation (eqn 1) ina POX reactor, for example. In addition, some total oxidation (eqn 2)may occur, and there may be a shift reaction (eqn 3). The reactions mayinclude:CH₄+½O₂→CO+2H₂—  (1)CH₄+2O₂→CO₂+2H₂O—  (2)The product synthesis gas from the POX reactions produces a very hightemperature gas mixture that may be used to provide part of theendothermic heat of reaction for steam/hydrocarbon reforming in asecondary downstream gas-heated catalytic reformer (EHTR). The remainingpart of the heat requirement is provided by mixing the product gas fromthe EHTR with the product gas from the POX prior to the total gas streambeing used to heat the EHTR. The steam reforming reactions may include:CH₄+H₂O→CO+3H₂—  (3)CO+H₂O→CO₂+H₂—  (4)

The synthesis gas stream 531 may include hydrogen and carbon monoxide.The synthesis gas stream 531 may also include unreacted feed components,water, carbon dioxide, argon, and/or nitrogen. The relativeconcentrations of carbon monoxide and hydrogen may depend, for example,on the hydrocarbon feed composition (e.g., methane is only used in theseequations for simplicity, but other components may be present in thefeed and be oxidized and/or reformed), pressure, and/or outlettemperature from the catalyst beds. The oxygen purity can be in therange 90 to near 100% by volume O₂ and, more particularly, can be in therange 95% to 99.5% O₂ by volume.

The objective of this process is to produce methanol directly from thesynthesis gas generation system at high purity. Reactions 1 to 3 areadversely affected by higher pressures, while reaction 4 is independentof pressure. Reactions 1 and 2 may compensate for higher pressure by arelatively small increase in reaction temperature, which may be achievedthrough a slight increase in the oxygen to hydrocarbon ratio. Theincrease in the oxygen to hydrocarbon ratio and the small increase intemperature will not cause significant problems in the design of theequipment.

In order for the EHTR system to operate as a steam/hydrocarbon reformingreactor at high pressures above 60 bar, the system 100 may use a veryhigh steam to active carbon ratio in the feed to the EHTR in order tocontrol the methane concentration in the synthesis gas product 407. Thisshould be above 5, and preferably in the range 5 to 10. The actual steamto active carbon ratio in the hydrocarbon feed to the GHR depends on thepressure and the EHTR catalyst tube outlet temperature. The ratio ischosen to limit the ratio of CH₄ to (H₂+CO) in the synthesis gas productleaving the EHTR tubes to a at least about 5% and preferably in therange 5% to 10% (molar). In order to compensate for the extra heat loadon the EHTR caused by the difference in temperature between the feed tothe EHTR tubes and the temperature of the product stream 407 leaving theshell side, the POX outlet temperature should be higher than a normalfigure of about 1340° C. The POX outlet temperature may be raised byincreasing the oxygen to hydrocarbon ratio in the POX feed so that thePOX outlet temperature is above 1400° C. and preferably in the range1425° C. to 1500° C. When using an ATR, the maximum outlet temperaturewill be in general below 1050° C. and in this case the ratio ofsynthesis gas from the ATR to that from the EHTR will be increased.

In order for the EHTR system to operate as a steam/hydrocarbon reformingreactor at high pressures (e.g., above 60 bar), a very high steam toactive carbon ratio in the feed may be used. Thus, for the production ofsynthesis gas, a higher methane content in the outlet gas from the EHTRand ATR will be produced. However, the outlet gas stream from the POXmay not have a higher methane content. Since about 70% of the syngas isproduced from the POX reactor and only about 30% from the GHR, it ispossible to tolerate a much larger CH₄ content in the EHTR outlet gasthan from, for example, a stand-alone steam/natural gas reformer.Although it is not possible to increase the outlet temperature from theATR, the outlet temperature of greater than 1000° C. means that the CH₄content will be less than 1%, so an increase caused by the desire toincrease the reaction pressure will not have a significant effect. Afurther characteristic of the EHTR design used in this process is thefact that the EHTR catalyst filled tubes are mounted in a verticalbundle with an inlet tube sheet at the top colder end, and with thebottom hot outlet ends open, so that the tubes are free to expanddownwards when heated to operating outlet temperatures, which will be inthe range 800° C. to 900° C. This means that the pressure differencebetween the inside and outside of the EHTR tubes, when operating atdesign conditions, is quite small. The sum of the pressure drop in thecatalyst filled tube plus the shell side pressure drop is a maximumvalue at the cold upper end of the EHTR tubes and approximately zero atthe bottom hot end of the tubes. The EHTR can operate at any pressure upto an economic limitation caused by the pressure vessel design and anypressure constraint in the gas purification system chosen caused by theprogressively higher gas pressure. This is quite different from asteam/natural gas reformer, where the furnace operates at nearatmospheric pressure, and the strength of the tubes imposes a pressurelimitation on the synthesis gas pressure which is generally below 35 to40 atm.

The total synthesis product gas stream 407 is at a temperature in therange 600° C. to 800° C. It is passed through a heat recovery steamboiler, which receives a boiler feedwater stream 429 and produces asteam stream 31. The cooled synthesis gas stream 8 is passed through themethanol converter 104. In some implementations, the syngas stream 408may be about 77 bars at a point immediately up-stream of the heatrecovery (reboilers 514). The stream 408 may include a very large amountof steam so a parallel heat exchanger 501 to the reboilers 514 mayproduce heating by the boiler feedwater stream point 428. The inlet feedwater stream from the pump point 426 may be preheated in an exchanger502, which may be placed in parallel with the loop condenser 518. Inaddition or alternatively, the heat exchanger 502 may be placed upstreamand in series with the loop condenser 518. The system 400 partiallyintroduces the stream 408 at the exit of the methanol converter 504 andpartly or wholly directly into heat exchanger 501. A water separator maybe located at point B to separate water condensed from the stream 408directly without diluting the methanol product and increasing separationcosts. The boiler feed water may be heated as described above. Thenatural gas stream point 447 will provide the fuel required by the firedheater burner supplemented by the purge gases produced in the methanolloop and the methanol distillation system.

These features may produce the CO+CO₂+H₂ feed gas for a low pressuremethanol synthesis system at a loop pressure in the range 50 to 100 barand at a temperature in the range 200° C. to 400° C., which be close tothe operating temperature of the methanol synthesis reactor 504.

The benefits of this invention are that it increases the overallefficiency of the methanol plant and reduces cost by operating thesynthesis gas system at high pressure thus reducing equipment size andcost, that it eliminates the conventional synthesis gas cooling andcompression system and that it introduces hot feed gas into the loop andallows extra by-product power production.

A gas turbine may drive an air compressor, which may provide the feedair stream to the ASU. A portion of the feed stream (e.g., natural gas)446 may be provided to the gas turbine as fuel. The gas turbine exhaust417 may be at approximately 450° C. The gas turbine exhaust 417, whichincludes oxygen, may be provided as the combustion air stream for thefired heater burner.

The fired heater may heat a first part 423 of the feed stream (e.g.,natural gas) to be provided to the POX. The first part 423 may becompressed, and the compressed first part 424 may be heated by the firedheater to produce a preheated feed stream 405 that is provided to thePOX. The fired heater may also heat a second part 420 of the feed streamto be provided to the EHTR. The second part 420 may be compressed, andthe compressed second part 421 may be heated in the fired heater toproduce a preheated feed stream 422 to be provided to the EHTR. Processwater 442, together with saturated steam stream 431, may also be heatedto produce multiple streams 444, 433, 432, and total superheated steamstream 434 of steam at 80 bar 500° C. for the process. The steam stream434 splits into stream 435, used for preheating the O₂ feed to the POXor ATR and streams 436 and 437, stream 436, is added to stream 422 toproduce the total feed gas steam 406 to the tube side of the EHTR, andstream 437, includes the remaining high pressure superheated steam,which is passed through a condensing steam turbine coupled to anelectric generator. Thus, through use of various streams for combustionand/or heat transfer, the thermal efficiency of the process may begreater than 60%. For example, the thermal efficiency of the process,based on the LHV of methanol product compared to total feed natural gas,may be greater than approximately 70% and can be above 75%.

In some implementations, at least a portion of the separated waste gasstreams, which may include inert gases and carbon oxides, may be used aspart of a fuel gas stream in a fired heater using as combustion air thegas turbine exhaust and/or an air stream. The heat generated may be usedto preheat the hydrocarbon and steam feeds to the synthesis gasgeneration units. Since a significant quantity of argon and nitrogen,which may be from the oxygen stream and/or feed streams, may be includedin the waste gas streams, a simple recycle of the CH₄/Ar/N₂ in streamsback to the feed point of the synthesis gas generation system may causea build-up of these components in the system. Thus, use of separatedwaste gas streams as fuel may reduce process waste streams and/orimprove cost-efficiency of processes (e.g., due to the recycle as fuel).

Although the feed stream is described as including methane, the feedstream may include other components such as other hydrocarbons (e.g.,ethane, propane, butane, pentane, benzene), other carbon and hydrogencontaining compounds (e.g., carbon dioxide, carbon monoxide, hydrogen,alcohols, etc.), organic compounds, nitrogen, argon, etc. The feedstream may be natural gas, gases associated with the production ofgasoline, combustible off-gasses from other processes, liquidhydrocarbons, etc. In some implementations, when the feed stream may beprocessed natural gas, for example, the sulfur compounds in natural gasmay be removed or at least partially removed to prevent catalyst damage.

Although the synthesis gas is described as including carbon monoxide andhydrogen, the synthesis gas may also include other components, such asinert gases (e.g., nitrogen or argon). In some implementations, carbonoxides may include oxides of carbon, such as carbon monoxide and carbondioxide. Although streams have been described to include variouscomponents in the implementations, the streams may include one or moreother components.

Various other implementations may be utilized in combination withsystems, such as system 400 illustrated in FIG. 1. In addition, varioussteps may be added, modified, and/or omitted. As an example, the carbondioxide separated from the product synthesis gas stream may be providedto other processes (e.g., urea production processes or as a compressedstream for sequestration.). Alternatively, a portion of the separatedCO₂ may be recycled back to the synthesis gas generation section andadded to the feed gas to the POX, ATR, or EHTR.

Although the above illustration includes various streams being heatedand/or compressed, other streams may be heated and/or compressed and/orshown streams may not be heated and/or compressed, as illustrated.

Although a specific implementation of the system is described above,various components may be added, deleted, and/or modified. In addition,the various temperatures and/or concentrations are described forexemplary purposes. Temperatures and/or concentrations may vary, asappropriate.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the implementations. Accordingly, otherimplementations are within the scope of this application.

It is to be understood the implementations are not limited to particularsystems or processes described which may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular implementations only, and is not intended to belimiting. As used in this specification, the singular forms “a”, “an”and “the” include plural referents unless the content clearly indicatesotherwise. Thus, for example, reference to “a reactor” includes acombination of two or more reactors and reference to “a feedstock”includes different types of feedstocks.

What is claimed is:
 1. A method for producing methanol, comprising;producing oxygen in an air separation plant with air compressors drivenby a gas turbine; heating a hydrocarbon feed stream using exhaust fromthe gas turbine; exothermically reacting a first portion of the heatedhydrocarbon feed stream with at least one of steam or an oxidant gascomprising molecular oxygen to produce an exothermically generatedsyngas product; endothermically reforming a second portion of thehydrocarbon feed stream with steam over a catalyst in a heat exchangereformer to produce an endothermically-reformed syngas product, whereinat least a portion of heat used in generation of theendothermically-reformed syngas product is obtained by recovering heatfrom the exothermically-generated syngas product and the endothermicallyreformed syngas product; combining the exothermically generated syngasproduct and the endothermically-reformed syngas product to produce acombined syngas stream; producing steam in a waste heat boiler bycooling the combined syngas stream, where the combined syngas streamleaving the waste heat boiler has a pressure from 70 bar to 100 bar;separating water from the cooled combined syngas to produce a methanolplant feed at substantially reaction loop pressure and having less thanabout 2% CH₄ and less than about 0.2% H₂O; after separating water,passing the cooled combined syngas to a methanol plant; and combiningmethanol plant combustible effluent with methane fuel to the gasturbine.
 2. The method of claim 1, wherein the exothermically-generatedsyngas product is generated using a partial oxidation burner followed bya catalytic reforming section in a convectively heated steam plushydrocarbon reformer.
 3. The method of claim 1, wherein the hydrocarbonfeed stream includes methane.
 4. The method of claim 1, wherein theexothermically generated syngas product has a temperature greater thanabout 1000° C.
 5. The method of claim 1, wherein the endothermicreforming occurs at a pressure of about 70 bars or greater.
 6. Themethod of claim 1, further comprising producing substantially puremethanol using the cooled combined syngas at a rate of about 700 metrictons per day.
 7. The method of claim 6, wherein the substantially puremethanol includes about 95% or greater methanol.
 8. The method of claim1, wherein the cooled combined syngas is passed to the methanol plantindependent of using a feed stream compressor.
 9. The method of claim 1,wherein the cooled combined syngas is passed to the methanol plant at apressure in a range from about 70 to 100 bars.
 10. The method of claim1, wherein the second portion of the hydrocarbon feed stream includes asteam to active carbon ratio in a range of about 5 to
 8. 11. The methodof claim 1, wherein a gas-heated catalytic reformer (GHR) produces theendothermically-reformed syngas product by using catalyst filled tubesmounted in a vertical bundle with an inlet tube sheet at a top end andopen bottom outlet ends.